#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <stack>

using namespace std;

vector<vector<long long> > graf;
vector<long long> ciclu;
vector<long long>::iterator it;
stack<long long>q;
long long n,m;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

void euler ()
{
    long long v,w;
    while(!q.empty())
    {
        v = q.top();
        if(!graf[v].size()){g<<v<<' ';q.pop();}
        else
        while(graf[v].size())
        {
            w = *graf[v].begin();

            graf[v].erase(graf[v].begin());
            it=find(graf[w].begin(), graf[w].end(), v);
            graf[w].erase(it);

            q.push(w);
        }
    }

}
int main()
{
    long long i,u,v;
    unsigned isEuler=1;
    f>>n>>m;
    graf.resize(n+1);
    for(i=1;i<=m;i++)
    {
        f>>u>>v;
        graf[u].push_back(v);
        graf[v].push_back(u);
    }
    for(i=1;i<=n;i++)
        if(graf[i].size()%2==1){
            isEuler=0;break;
        }

    q.push(1);
    if(isEuler)euler();
    else g<<-1;
    return 0;
}